Method for Adjusting Metal Polishing Rate and Reducing Defects Arisen in a Polishing Process

ABSTRACT

The invention discloses a method for adjusting metal polishing rate and reducing defects arisen in a polishing process, in which a electric conduction system is additionally provided to a polishing apparatus to electrify the polishing fluid; in the polishing process, the polishing fluid flows through the polishing pad and the wafer to be polished, such that the polished metal surface of the wafer is electrically charged so as to control the oxidation of the polished metal surface of the wafer. The invention has solved the problem that the dishing and erosion defects are prone to be formed in the existing polishing process, the potential of the polishing fluid is changed by means of the additional electric conduction system and thus the polishing rate of the polished metal is controlled so as to reduce the dishing and erosion defects occurred in the polishing process.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is based upon and claims priority under 35U.S.C. §119 to prior Chinese Patent Application No. 201110110366.0 filedon Apr. 29, 2011, the entire contents of which are incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates to a semiconductor metal polishingtechnique, and more particularly, to a method for adjusting metalpolishing rate and reducing defects arisen in a polishing process.

BACKGROUND

In the manufacture of wafers, as the upgrading of the process technologyand the reduction of sizes of wires and grids, the lithograph technologyhas an increasing demand for non-uniformity of the wafer surface. IBMdeveloped and introduced CMOS products in 1985, and successfully appliedCMOS in manufacturing 64 MB DRAM in 1990. CMP (Chemical MechanicalPlanarization) has been developed rapidly since 1995 and is used widelyin semiconductor industry.

A polishing mechanism, taken copper polishing which is necessary in anadvanced process for instance, is mainly based on an oxidation reactionof copper in a polishing fluid as follows:

1. If copper is at a relative high potential in the polishing fluid,copper will easily react with chemical compositions in the fluid togenerate oxide(s) or copper ion(s);

2. If copper is at a relative low potential, its oxidation will beweaken or suppressed; contrary, such reaction is accelerated at a higherpotential.

At present, the commonly used polishing stands perform polishing by africation effect between a polishing pad and a wafer under the influenceof a polishing fluid. Referring to FIG. 1, which is a schematicstructural diagram of a polishing stand according to the prior art,since the polishing rate is different for different mediums, defects ofso-called dishing and erosion are often caused. In view of processquality, a low-pressure polishing is usually used in the practicalproduction for a better result. However, the pressure will have animpact on the polishing rate also, a low pressure corresponds to a lowerpolishing rate, which would not facilitate the improvement ofproductivity and the reduction of cost.

Chinese patent Application No. 200780041698.X, entitled “Method andApparatus for Electrochemical Mechanical Polishing Nip Substrates”disclosed a method for accelerating polishing of a Nip substrate.However, the document does not relate to the area of producing anintegrated circuit, but only refers to polishing Nip substrate.Obviously, the integrated circuit process requires a more accurateprocess control, and the metal polishing in the integrated circuitprocess is not suitable to be performed by using asingle-directional/single-magnitude current or voltage. Moreover, thedocument does not relate to the phenomenon of cathodic protectionresulted from the change of a current direction.

SUMMARY OF THE INVENTION

The present invention discloses a method for adjusting metal polishingrate and reducing defects arisen in a polishing process to solve theproblem that dishing and erosion defects are prone to be formed in theexisting polishing process.

The above object of the invention is achieved by the following technicalsolutions:

The invention provides a method for adjusting metal polishing rate andreducing defects arisen in a polishing process, comprising steps of:adding an electric conduction system to a polishing apparatus in orderto electrify a polishing fluid; and in the polishing process, making thepolishing fluid flow through a polishing pad and a wafer to be polished,such that a polished metal surface of the wafer is electrically chargedand thereby an oxidation of the polished metal surface of the wafer iscontrolled.

The aforementioned method for adjusting metal polishing rate andreducing defects arisen in a polishing process may further comprise:providing a conducting element layer inside of a polishing turntable forpolishing the wafer in the polishing apparatus, an edge portion of theconducting element layer being exposed to outside of a side edge of thepolishing turntable, and the polishing fluid, when flowing down aroundthe polishing turntable, contacting the conducting element layer.

According to the aforementioned method for adjusting metal polishingrate and reducing defects arisen in a polishing process, the conductingelement layer may be grounded.

According to the aforementioned method for adjusting metal polishingrate and reducing defects arisen in a polishing process, the electricconduction system may provide a high potential to the polishing fluid,and the polished metal surface is at a higher potential in the polishingfluid, such that a reaction of the polished metal surface with chemicalcompositions in the polishing fluid is accelerated to generate metaloxide(s) or metal ion(s), and the accelerated oxidation reaction of themetal surface in turn results in an increased polishing rate, such thata scratch degree of the metal surface and a polishing pressure arereduced.

According to the aforementioned method for adjusting metal polishingrate and reducing defects arisen in a polishing process, the electricconduction system may provide a low potential to the polishing fluid,and the polished metal surface is at a lower potential in the polishingfluid. In such case, ions in the polishing fluid can suppress thereaction of the polished metal surface with the chemical compositions inthe polishing fluid, so that the metal polishing rate is reduced and amore flat surface is thereby obtained.

The invention also provides an apparatus for adjusting metal polishingrate and reducing defects arisen in a polishing process, comprising apolishing stand, wherein the polishing stand is provided with anelectric conduction system, and the electric conduction system has avoltage output terminal to contact the polishing fluid of the polishingstand.

In the aforementioned apparatus for adjusting metal polishing rate andreducing defects arisen in a polishing process, a conducting elementlayer may be provided inside of a polishing turntable of the polishingstand. The conducting element layer has an edge portion which is exposedto the outside of a side edge of the polishing turntable, and theconducting element layer has a leading-out terminal which is grounded.

To sum up, as the above technical solutions are introduced, the presentinvention has solved the problem that the dishing and erosion defectsare prone to be formed in the existing polishing process, the potentialof the polishing fluid is changed by means of the additionally arrangedelectric conduction system and thus the polishing rate of the polishedmetal is controlled, so as to achieve the object of reducing the dishingand erosion defects occurred in the polishing process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of a polishing stand accordingto the prior art;

FIG. 2 is a schematic structural diagram of an apparatus for adjusting ametal polishing rate and reducing defects arisen in a polishing processaccording to the invention;

FIG. 3 is a schematic structural diagram of the apparatus for adjustingmetal polishing rate and reducing defects arisen in a polishing processaccording to a first embodiment of the invention;

FIG. 4 is a schematic structural diagram of the apparatus for adjustingmetal polishing rate and reducing defects arisen in a polishing processaccording to a second embodiment of the invention;

FIG. 5 is a schematic structural diagram of a wafer beforemetal-polishing by means of the apparatus of the apparatus for adjustingmetal polishing rate and reducing defects arisen in a polishing processaccording to the invention;

FIG. 6 is a schematic structural diagram of a wafer after polishing bymeans of a polishing process according to the prior art;

FIG. 7 is a schematic structural diagram of a wafer after the metalpolishing by means of the apparatus for adjusting metal polishing rateand reducing defects arisen in a polishing process according to theinvention; and

FIG. 8 is a graph of voltage versus PH of copper.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the embodiments of the invention will be described indetail with reference to the appended drawings.

FIG. 2 is a schematic structural diagram of an apparatus for adjusting ametal polishing rate and reducing defects arisen in a polishing processaccording to the invention. Refer to FIG. 2, a method for adjusting ametal polishing rate and reducing defects arisen in a polishing processaccording to the invention may comprise a step of adding an electricconduction system 401 to the polishing apparatus. The electricconduction system 401 provides an additional current and electricalfield, and is connected to a polishing fluid outlet 301 of a polishingstand of the polishing apparatus in order to electrify a polishing fluid302 from the outlet 301. In the polishing process, the polishing fluid302 flows down from the polishing fluid outlet 301, and flows through apolishing pad 103; a wafer 201 is mounted on a wafer bracket 202, and asurface of the wafer 201 to be polished is pressed against the polishingpad 103 due to a pressure applied by the wafer bracket 202; the waferbracket 202 rotates the wafer 201 while a polishing turntable 102rotates the polish pad 103, wherein a rotation direction of the wafer201 is opposite to that of the polishing pad 103, so that the wafer 201can be polished. In the polishing process, the electrified polishingfluid 302 flows between the polishing pad 103 and the polished metalsurface of the wafer 201, so that the polished metal surface of thewafer 201 is electrically charged. When the surface of the wafer 201 ispolished to a different medium, because it is difficult to control themetal removal rate, dishing and erosion defects are prone to be formed;whereas after the surface of the wafer 201 is electrically charged, apotential of the surface of the wafer 201 will be changed (if thesurface of the wafer is polished to a different medium), a chemicalreaction on the polished metal surface of the wafer 201 may becontrolled accordingly, such that the metal polishing rate iscontrollable. Once the metal on the surface of the wafer 201 iselectrically charged, the metal surface can be protected, as a result,the dishing and erosion defects can be reduced in the polishing process.

The method according to the invention may further comprise a step ofproviding a conducting element layer 501 inside of the polishingturntable 102 of the apparatus. An edge portion of the conductingelement layer 501 is exposed to outside of a side edge of the polishingturntable 102. The polishing fluid 302, when flowing down around thepolishing turntable 102, contacts the conducting element layer 501 tomake the conducting element layer 501 be grounded, so as to maintain apotential of the polished metal surface of the wafer 201 stable. As aresult, stability of the polishing rate can be guaranteed. The polishingfluid 302 in the invention is an electrolyte fluid.

FIG. 8 is a graph of voltage vs. PH of copper. As shown from FIG. 8, thepolishing mechanism of the copper polishing, which is taken as anexample and is necessary in an advanced process, is mainly based on anoxidation reaction of copper in the polishing fluid: if copper is at arelative high potential in the polishing fluid, it can easily react withchemical compositions in the polishing fluid to generate oxide(s) orcopper ion(s); if copper is at a relative low potential, the oxidationof copper will be weakened or suppressed, contrarily, such reaction willbe accelerated at a higher potential.

The electric conduction system 401 according to the invention has afunction of adjusting the potential of the polishing fluid 302. That is,in different processing steps, the electric conduction system mayprovide the surface of the wafer 201 with a different potential, so thatthe potential of the surface of the wafer 201 can be adapted to variousprocessing step. When the polishing is processed to a certain stage, thesurface metal of the wafer 201 may be brought to a low potential inorder to reduce the metal polishing rate, so as to achieve an effect ofreducing dishing and erosion defects. If the surface metal of the wafer201 is brought to a high potential, the metal polishing rate isincreased, so the pressure on the wafer 201 may be reduced, as a result,the effect of reducing the dishing and erosion defects can also beachieved.

FIG. 3 is a schematic structural diagram of the apparatus for adjustingmetal polishing rate and reducing defects arisen in a polishing processaccording to a first embodiment of the invention. Refer to FIG. 3,according to the first embodiment of the invention, in the polishingprocess of the polished metal surface of the wafer 201, the electricconduction system 401 provides a high potential to the polishing fluid302, so in the polishing fluid 302, the polished metal surface is at arelative high potential, which accelerates a reaction of the polishedmetal surface with chemical compositions in the polishing fluid 302 togenerate metal oxide(s) or metal ion(s). In turn, the acceleratedoxidation reaction of the metal surface results in an increasedpolishing rate, such that the polishing pressure is reduced, and ascratch degree of the metal surface is reduced as well.

FIG. 4 is a schematic structural diagram of the apparatus for adjustingmetal polishing rate and reducing defects arisen in a polishing processaccording to a second embodiment of the invention. Refer to FIG. 4, inthe polishing process of the polished metal surface of the wafer 201according to the second embodiment of the invention, contrary to thefirst embodiment, the electric conduction system 401 provides a lowpotential to the polishing fluid 302, so in the polishing fluid 302, themetal surface being polished is at a relative low potential. In suchcase, ions in the polishing fluid 302 suppress the reaction of thepolished metal surface with the chemical compositions in the polishingfluid, so that the metal polishing rate is reduced and a more flat(polished) surface is thereby obtained.

FIG. 2 is a schematic structural diagram of the apparatus for adjustingmetal polishing rate and reducing defects arisen in a polishing processaccording to the invention. Refer to FIG. 2, the apparatus for adjustingmetal polishing rate and reducing defects arisen in a polishing processcomprises a polishing stand 101 provided with an electric conductionsystem 401. The electric conduction system 401 has a voltage outputterminal to contact the polishing fluid outlet 301 of the polishingstand 101, so that the polishing fluid 302 is electrically charged, as aresult, the polishing fluid 302 flows between the polishing pad 103 andthe wafer 201 in the polishing process and makes the polished metalsurface of the wafer be electrically charged, which produces an effectof controlling the metal polishing rate.

A conducting element layer 501 is provided inside of the polishingturntable 102 of the polishing stand 101 according to the invention. Theconducting element layer 501 has an edge portion which is exposed tooutside of the side edge of the polishing turntable 102, and has aleading-out terminal 502 which is grounded in order to maintain thestability of the potential of the surface of the wafer 201.

FIG. 5 is a schematic structural diagram of a wafer beforemetal-polishing which is performed by the apparatus for adjusting metalpolishing rate and reducing defects arisen in a polishing processaccording to the invention, and FIG. 6 is a schematic structural diagramof a wafer after polishing by means of a polishing process according tothe prior art. Refer to FIGS. 5 and 6, it can be clearly seen that thesurface of the wafer, after the polishing process of the prior art,dishing defect and erosion defect appear. FIG. 7 is a schematicstructural diagram of a wafer after metal-polishing which is performedby the apparatus for adjusting metal polishing rate and reducing defectsarisen in a polishing process according to the invention. As shown inFIG. 7, the wafer polished through the etching process of the inventionhas a very flat surface, and the dishing and erosion defects areeffectively eliminated.

To sum up, by the above technical solutions, the invention has solvedthe problem that the dishing and erosion defects are prone to be formedin the existing polishing process, and by additionally providing theelectric conduction system to change the potential of the polishingfluid and in turn control the polishing rate of the metal beingpolished, the invention has achieved the object of reducing the dishingand erosion defects occurred in the polishing process.

The specific embodiments of the invention have been described above,however, they are exemplifications only, and the invention does notintend to be limited to the above specific embodiments. For the personskilled in the art, any equivalent modification or substitution to theinvention would fall into the scope of the invention. Therefore, anyequivalent variation or modification that is made without departing fromthe spirit and scope of the invention should be covered by the scope ofthe invention.

1. A method for adjusting metal polishing rate and reducing defectsarisen in a polishing process, comprising steps of: adding an electricconduction system to a polishing apparatus in order to electrify apolishing fluid; and in the polishing process, electrically charging apolished metal surface of a wafer to be polished by the polishing fluidflowing through a polishing pad and the wafer, and thereby controllingan oxidation of the polished metal surface of the wafer.
 2. The methodfor adjusting metal polishing rate and reducing defects arisen in apolishing process according to claim 1, further comprising a step ofproviding a conducting element layer inside of a polishing turntable forpolishing the wafer in the polishing apparatus, wherein an edge portionof the conducting element layer is exposed to outside of a side edge ofthe polishing turntable, and the polishing fluid, when flowing downaround the polishing turntable, contacts the conducting element layer.3. The method for adjusting metal polishing rate and reducing defectsarisen in a polishing process according to claim 1, wherein theconducting element layer is grounded.
 4. The method for adjusting metalpolishing rate and reducing defects arisen in a polishing processaccording to claim 1, wherein the electric conduction system provides ahigh potential to the polishing fluid, and the polished metal surface isat a higher potential in the polishing fluid, so as to accelerate areaction of the polished metal surface with chemical compositions in thepolishing fluid to generate metal oxide(s) or metal ion(s), and theaccelerated oxidation reaction of the metal surface in turn results inan increased polishing rate, such that a scratch degree of the metalsurface and a polishing pressure are reduced.
 5. The method foradjusting metal polishing rate and reducing defects arisen in apolishing process according to claim 1, wherein the electric conductionsystem provides a low potential to the polishing fluid, and the polishedmetal surface is at a lower potential in the polishing fluid, and ionsin the polishing fluid suppress a reaction of the polished metal surfacewith chemical compositions in the polishing fluid, so that the metalpolishing rate is reduced and a more flat surface is thereby obtained.6. An apparatus for adjusting metal polishing rate and reducing defectsarisen in a polishing process, comprising a polishing stand, wherein thepolishing stand is provided with an electric conduction system, and theelectric conduction system has a voltage output terminal to contact apolishing fluid of the polishing stand.
 7. The apparatus for adjustingmetal polishing rate and reducing defects arisen in a polishing processaccording to claim 6, wherein a conducting element layer is providedinside of a polishing turntable of the polishing stand, and has an edgewhich is exposed to outside of a side edge of the polishing turntableand a leading-out terminal which is grounded.